Step stool



FIG. 1 is a perspective view of a step stool illustrating our new design;

FIG. 2 is a right-side elevational view thereof, with the left-side elevational view thereof substantially similar;

FIG. 3 is a top plan view thereof;

FIG. 4 is a front elevation view thereof; and,

FIG. 5 is a rear elevation view thereof. 

The ornamental design for a step stool, as shown and described. 